Autoleveller draw frame, method for operating an autoleveller draw frame, and method for converting an autoleveller draw frame

ABSTRACT

An autoleveller draw frame includes a drafting system having a plurality of roller combinations. A drive unit configured with the plurality of roller combinations has a main motor that drives a first roller combination at a constant main rotational speed. A regulating motor regulates a rotational speed of a second roller combination wherein, due to the regulation, the rotational speed of the second roller combination is changeable from a basic rotational speed into an autolevelling speed. The basic rotational speed depends on the main rotational speed and the autolevelling speed is independent of the main rotational speed, wherein the drafting of the fibrous web is adjustable. The regulating motor is drive-independent of the main motor to drive the second roller combination at the autolevelling speed according to an electrical signal that is based on the main rotational speed.

FIELD OF THE INVENTION

The present invention relates to an autoleveller draw frame having adrafting system, which includes multiple roller combinations situatedone behind the other for drafting a fibrous web to be processed, andhaving a drive unit for driving the multiple roller combinations. Thedrive unit including: a main motor for the speed-constant driving of atleast one first roller combination at a main rotational speed, and aregulating motor for regulating the rotational speed of at least onesecond roller combination, wherein, due to the regulation, therotational speed of the second roller combination is changeable from abasic rotational speed, which depends on the main rotational speed, intoan autolevelling speed, which is independent of the main rotationalspeed, and, in this way, the draft of the fibrous web is adjustable. Theinvention further relates to a method for operating an autoleveller drawframe and to a method for converting an autoleveller draw frame.

BACKGROUND

EP 2 149 628 A1 describes an autoleveller draw frame, which has a mainmotor for driving at least two roller combinations and a regulatingmotor for the superimposed driving of at least one of the rollercombinations. A basic rotational speed of the main motor can besuperimposed on by the regulating motor by means of a differential gear,which is connected on one side to the main motor and on the other sideto the regulating motor. This has the disadvantage that the differentialgear is highly maintenance-intensive and, in particular as the period ofoperation increases, is highly susceptible to failure. In addition, themaintenance and/or replacement of the main motor and/or regulating motorused here are/is very highly technically complex.

SUMMARY OF THE INVENTION

A problem addressed by the present invention is that of eliminating thedisadvantages known from the prior art. Additional objects andadvantages of the invention will be set forth in part in the followingdescription, or may be obvious from the description, or may be learnedthrough practice of the invention.

The problems are solved by an autoleveller draw frame, a method foroperating an autoleveller draw frame, and a method for converting anautoleveller draw frame having the features described and claimedherein.

The invention provides an autoleveller draw frame having a draftingsystem, which includes multiple roller combinations situated one behindthe other for drafting a fibrous web to be processed, and having a driveunit for driving the multiple roller combinations. Roller pairs made upof two rollers and/or arrangements made up of three rollers are usuallyused as the roller combinations. The drafting system usually has threeroller combinations, wherein these roller combinations can be referredto as an input roller combination, a middle roller combination, and anoutput roller combination. A plurality of slivers usually enters theinput roller combination, in which the fibrous web to be processed isformed by compressing the incoming slivers. Thereafter, the fibrous webis drafted in the drafting system, the input roller combination and themiddle roller combination usually forming a pre-drafting field. Themiddle roller combination and the output roller combination usually forma main drafting field.

The drive unit includes a main motor for the speed-constant driving ofat least one first roller combination at a main rotational speed.Moreover, the drive unit includes a regulating motor for regulating therotational speed of at least one second roller combination, wherein, dueto the regulation, the rotational speed of the second roller combinationis changeable from a basic rotational speed, which depends on the mainrotational speed, into an autolevelling speed, which is independent ofthe main rotational speed, and, in this way, the draft of the fibrousweb is adjustable. Preferably, the main motor drives the output rollercombination such that the output roller combination is operated at aconstant rotational speed and at a constant delivery speed. Theregulating motor preferably drives the input roller combination and/orthe middle roller combination.

According to the invention, the regulating motor is drive-independent ofthe main motor and drives the second roller combination independently ofthe main motor at the autolevelling speed on the basis of an electricalsignal, which depends on the main rotational speed. “Drive-independent”is to be understood to mean that the rotational movement of theregulating motor is mechanically independent of the main motor. Therespective output elements of the regulating motor and of the main motorare independent of one another with respect to their rotationalmovement.

The basic rotational speed of the regulating motor depends directly onthe main rotational speed of the main motor. The electrical signal,which depends on the main rotational speed, is transmitted directly orindirectly from the main motor to the regulating motor. The regulatingmotor is driven at the autolevelling speed on the basis of thiselectrical signal, wherein the autolevelling speed can differ from thebasic rotational speed.

As described above, the main motor drives the at least one first rollercombination at the constant main rotational speed. The basic rotationalspeed of the regulating motor is based on the main rotational speed ofthe main motor. If the regulating motor drives the at least one secondroller arrangement at the basic rotational speed, the autoleveller drawframe is operated with a predefined draft. In order to change the draftin the drafting system, the basic rotational speed can therefore bereplaced by a changeable autolevelling speed.

Due to the fact that the regulating motor drives the second rollerarrangement on the basis of the electrical signal, which depends on themain rotational speed, a mechanical transmission of the rotationalspeed, for example by means of belt drives, is not necessary. Acomplicated drive unit having a differential gear can therefore bedispensed with. The electrical signal can also be very easilymanipulated in order to adapt and/or change the autolevelling speedand/or the basic rotational speed.

It is advantageous when the drive unit includes a speed sensor fordetecting the rotational speed of the at least one first rollercombination and/or of the main motor. The speed sensor can thereforedetect the main rotational speed of the first roller combinationdirectly at the first roller combination and/or calculate this on thebasis of the rotational speed of the main motor. As a result, the mainrotational speed can be very easily and precisely determined. Inaddition, when converting an autoleveller draw frame having a mechanicaldifferential gear, an existing speed sensor can be reused and/or thespeed sensor can be easily retroactively installed.

It is also advantageous when the drive unit has at least onetransmission unit for transforming the rotational speed detected by thespeed sensor into the basic rotational speed of the second rollercombination. The detected rotational speed can be the main rotationalspeed and/or the rotational speed of the main motor, as described above.The transmission unit transforms the detected rotational speed with aconstant gear ratio such that the basic rotational speed formedtherefrom depends directly on the main rotational speed. Alternatively,the transmission unit can be integrated in the speed sensor such thatthe speed sensor outputs the basic rotational speed as an electricalsignal. The basic rotational speed of multiple second rollercombinations, such as, for example, of an input roller combination andof an output roller combination, can differ from one another.Transmission elements and/or belt drives, for example, can be used totransform the rotational speeds.

It is advantageous when the autoleveller draw frame includes a pair ofscanning rollers for detecting the thickness of at least one sliverentering the drafting system. The pair of scanning rollers is installedupstream from the input roller combination such that the thickness ofthe at least one incoming sliver can be determined before a fibrous webis formed from the sliver.

It is also advantageous when the autoleveller draw frame includes aspecification unit, which is electrically operatively connected to thepair of scanning rollers and specifies a superimposition speed and/ordetermines a superimposition speed from the thickness of the at leastone sliver. As described above, the draft of the drafting system isadjusted on the basis of the thickness of the incoming slivers. Thesuperimposition speed can be ascertained by means of the specificationunit from the thickness measured by the pair of scanning rollers, whichsuperimposition speed is necessary in order to be superimposed on thebasic rotational speed of the regulating motor in order to obtain auniform draft or the desired draft of the fibrous web.

Moreover, it is advantageous when the drive unit includes a control unitfor calculating the autolevelling speed and/or for controlling theregulating motor. The control unit preferably adds the basic rotationalspeed output by the transmission unit to the superimposition rotationalspeed output by the specification unit. Moreover, it is conceivable thatthe control unit is operatively connected to a quality sensor installeddownstream from the drafting system such that the drafted sliver ischecked for quality before being placed into the can. In this way, forexample, the autolevelling speed can be adjusted on the basis of thequality of the drafted sliver.

It is also advantageous when the drive unit includes at least onetransmission line for transmitting the electrical signal between theregulating motor, the main motor, the speed sensor, the transmissionunit, the pair of scanning rollers, the specification unit and/or thecontrol unit. The transmission line can be used for transmitting theelectrical signal. It is also conceivable for the signal transmission tobe carried out by means of a transceiver such that the electrical signalis transmitted wirelessly or by radio.

It is also advantageous when the control unit is electricallyoperatively connected to the specification unit, the transmission unitand/or the regulating motor such that the autolevelling speed iscalculated from the superimposition speed and the basic rotational speedand/or is transmitted to the regulating motor as an electrical signal.

It is also advantageous when the main motor is formed as an inductionmotor and/or the regulating motor is formed as a reluctance motor. Themain motor in the form of an induction motor has the advantage that thisholds the rotational speed nearly constant. In addition, this has a veryrobust configuration and can be cost-effectively manufactured. Theregulating motor in the form of a reluctance motor, in particular asynchronous reluctance motor, has the advantage that this has a simpleand uncomplicated configuration and, thereby, can be operated reliablyand in a cost-effective manner. The synchronous reluctance motor ispreferably operated with a frequency inverter, which is arranged, forexample, in the control unit. As a result, very high efficiency can beachieved.

Moreover, a method for operating an autoleveller draw frame is provided.In the method, a fibrous web to be processed is drafted using a draftingsystem, which includes multiple roller combinations situated one behindthe other and the multiple roller combinations are driven by means of adrive unit. A main motor of the drive unit drives at least one firstroller combination at a main rotational speed. A regulating motor of thedrive unit regulates the rotational speed of at least one second rollercombination, wherein, due to the regulation, the rotational speed of thesecond roller combination is changed from a basic rotational speed,which depends on the main rotational speed, into an autolevelling speed,which is independent of the main rotational speed, and, in this way, thedraft of the fibrous web is adjustable.

According to the invention, the regulating motor drives the secondroller combination drive-independently of the main motor at theautolevelling speed on the basis of an electrical signal, which dependson the main rotational speed.

Due to the fact that the regulating motor drives the second rollerarrangement on the basis of the electrical signal, which depends on themain rotational speed, a mechanical transmission of the rotational speedis not necessary. As described above, a differential gear is no longerrequired in the drive unit. As a result, the mechanical transmission ofthe rotational speed from the main motor to the second rollercombination is dispensed with. In addition, the electrical signal can bevery easily manipulated in order to adapt and/or change theautolevelling speed and/or the basic rotational speed.

It is advantageous when the autoleveller draw frame is designedaccording to the preceding description and/or the following description,wherein the aforementioned features can be present individually or inany combination.

Moreover, a method for converting an autoleveller draw frame isprovided. The autoleveller draw frame in this method for conversionincludes a drafting system, which has multiple roller combinationssituated one behind the other for drafting a fibrous web to beprocessed. In addition, the autoleveller draw frame includes a driveunit for driving the multiple roller combinations. The drive unitincludes a main motor for the speed-constant driving of at least onefirst roller combination at a main rotational speed. The drive unit alsoincludes a differential gear for transmitting the rotational speed ofthe main motor to at least one second roller combination such that abasic rotational speed of the second roller combination depends on themain rotational speed of the first roller combination. In addition, thedrive unit includes a superimposition motor for superimposing asuperimposition speed on the basic rotational speed by means of adifferential gear such that, due to the superimposition, the rotationalspeed of the at least one second roller combination is changeable fromthe basic rotational speed into an autolevelling speed and, in this way,the draft of the fibrous web is adjustable.

The differential gear is preferably formed as a planetary gear thatenables a three-shaft operation. The differential gear has a first driveelement, which is driven by the main motor. A second drive element ofthe differential gear is driven by the superimposition motor. The atleast one second roller combination can be driven by means of an outputelement of the differential gear.

According to the invention, the differential gear is removed from thedrive unit and the superimposition motor is replaced by a regulatingmotor that is drive-independent of the main motor. After installationinto the autoleveller draw frame, the regulating motor drives the secondroller combination independently of the main motor at the autolevellingspeed on the basis of an electrical signal, which depends on the mainrotational speed.

Due to the above-described changes in the drive unit of the autolevellerdraw frame, the mechanical differential gear, which is susceptible tofailure, can be removed. Thereafter, the regulating motor mechanicallydrives the second roller combination independently of the main motor,and therefore a superimposition on the rotational speeds is no longernecessary. This results in a lower-maintenance operation of theautoleveller draw frame after the conversion.

It is advantageous when the autoleveller draw frame, after theconversion, is designed according to the preceding description, whereinthe aforementioned features can be present individually or in anycombination.

It is also advantageous when at least one drive element and/or outputelement of the differential gear are/is reused as a transmission elementof the regulating motor. Drive elements are understood to be elements ofthe differential gear, which is removed during the conversion, at whichthe main motor and/or the superimposition motor drive(s) thedifferential gear. These types of drive elements can be, for example,drive shafts and/or driving pulleys. These types of drive elements arefrequently connected to the superimposition motor and/or to the mainmotor by means of drive belts. An output element is understood to be anelement that connects the differential gear to the second rollercombination and drives the second roller combination. An additional beltdrive for transforming the rotational speed can also be provided here.

In the mechanical differential gear, the at least one drive elementand/or output element can be designed to set or adjust the ratio.Different sizes of the at least one drive element and/or output elementcan result in different rotational speeds of the second rollercombination. This can be necessary for adjusting the main draft and/orthe pre-draft, for example, when changing the material of the sliver orof the slivers. This adjustment of the main draft and/or of thepre-draft is independent of the autolevelling and, therefore, is apermanent change in the draft.

A transmission element of the regulating motor is to be understood to bean element that is slid directly onto the regulating motor or isarranged indirectly between the regulating motor and the at least onesecond roller combination such that the transmission element cantransform the rotational speed toward the second roller combination. Dueto the reuse of the at least one drive element and/or output element asa transmission element of the regulating motor, the permanent gearratios, which are used in the autoleveller draw frame having thedifferential gear and the superimposition motor, can be very easilyadapted to the autoleveller draw frame having an independent regulatingmotor.

It is also advantageous when a mechanical or electromagnetic brake ordrive unit is removed. The brake is usually used to decelerate thesuperimposition motor so that the at least one second roller combinationis operated at its basic rotational speed. Since the superimpositionmotor is removed, the brake is also no longer required and therotational speed can be electrically controlled. For this purpose, thecontrol unit is used to regulate the rotational speed. Therefore, withthe brake, one further wearing device (in addition to the differentialgear) can be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are described in the followingexemplary embodiments, wherein:

FIG. 1 shows a schematic view of an autoleveller draw frame according tothe prior art, and

FIG. 2 shows a schematic view of an autoleveller draw frame according tothe invention.

DETAILED DESCRIPTION

In the following description of the alternative exemplary embodimentsrepresented in the figures, the same reference signs are utilized forfeatures that are identical or at least comparable in terms of theirconfiguration and/or mode of operation. Provided the features are notdescribed in detail again, their design and/or mode of operationcorrespond/corresponds to the design and mode of operation of theabove-described features. For the sake of greater clarity, referencesigns for previously described components have not been individuallyincluded in the figures.

FIG. 1 shows a schematic view of an autoleveller draw frame 1 accordingto the prior art. In the autoleveller draw frame 1, one or multiplesupplied sliver(s) 2 is/are evened out and drafted and, thereafter,deposited in a can (not shown here), in a known way. The slivers 2 aresupplied to a drafting system 4 via a pair of scanning rollers 3. It isalso possible that the slivers 2, before being supplied to the pair ofscanning rollers 3, are condensed to form one sliver 2 by means of acondenser (not shown here). The drafting system 4 includes multipleroller combinations 6, 6′, 6″, which are situated one behind the other.The roller combinations 6, 6′, 6″ are designed to draft a fibrous web 7,which is formed from the at least one sliver 2.

The roller combinations 6, 6′, 6″ can be formed as roller pairs havingtwo rollers or as a roller combination having three rollers. In theexemplary embodiment shown, three roller combinations 6, 6′, 6″ arepresent in the form of an input roller combination 6, a middle rollercombination 6′ and an output roller combination 6″.

The input roller combination 6 and the middle roller combination 6′ forma pre-drafting field. The middle roller combination 6′ and the outputroller combination 6″ form a main drafting field. All rollercombinations 6, 6′, 6″ are driven by a drive unit 8.

The output roller combination 6″ in the exemplary embodiment shown isdriven as the first roller combination 6″ at a constant rotational speedby means of a main motor 9 of the drive unit 8. The output rollercombination 6″ rotates at a constant main rotational speed. The inputroller combination 6 and the middle roller combination 6′ are formed asa second roller combination 6, 6′, respectively, and are regulated.

As described above, the exemplary embodiment from FIG. 1 is theautoleveller draw frame 1 according to the prior art, in which adifferential gear 10 transmits the rotational speed of the output rollercombination 6″ to the input roller combination 6 and to the middleroller combination 6′ such that a basic rotational speed of the inputroller combination 6 and of the middle roller combination 6′ depends onthe main rotational speed of the output roller combination 6″. Thedifferential gear 10 can be formed, for example, as a planetary gear.

The differential gear 10 includes a first drive element 11, a seconddrive element 12 and an output element 13. A constant rotational speedis introduced by the main motor 9 by means of the first drive element11. By means of this constant rotational speed, the input rollercombination 6 and the middle roller combination 6′ can be driven at thebasic rotational speed. A superimposition speed can be introduced by asuperimposition motor 14 by means of the second drive element 12. Due tothe superimposition speed being superimposed on the basic rotationalspeed, the input roller combination 6 and the middle roller combination6′ can be driven at an autolevelling speed. The autolevelling speed isthus essentially the sum of the basic rotational speed and thesuperimposition speed. For this purpose, the input roller combination 6and the middle roller combination 6′ are connected to the output element13.

Different rotational speeds can be achieved by means of different driveshafts of the roller combinations 6, 6′, 6″, as a result of which thebasic rotational speed and/or the autolevelling speed of the regulatedroller combinations 6, 6′ can differ from one another. Additional gearstages and/or belt drives can also lead to the individual rollercombinations 6, 6′, 6″, as a result of which the rotational speeds candiffer.

Changing the superimposition speed and, as a result, the levellingspeed, allows the draft of the fibrous web 7 to be adjustable andchangeable. Changing the autolevelling speed therefore results, inparticular, in a change in the main draft from the middle rollercombination 6′ to the output roller combination 6″. The thickness of theincoming slivers 2 is detected by the pair of scanning rollers 3. Thepair of scanning rollers 3 is electrically operatively connected to aspecification unit 15, which specifies the superimposition speed for thesuperimposition motor 14 and/or determines this from the thickness ofthe sliver 2. The specification unit 15 is also electrically operativelyconnected to the superimposition motor 14.

In addition, the drive unit 8 has a brake 16 in the area of thedifferential gear 10 or between the differential gear 10 and thesuperimposition motor 14, which can, in particular, completelydecelerate the superimposition motor 14 and/or the second drive element12. In this way, the current rotational speed of the input rollercombination 6 and of the middle roller combination 6′ can be deceleratedtoward the basic rotational speed as quickly as possible.

It is also pointed out that the view of the drive unit 8 from FIG. 1 andalso of the following FIG. 2 are highly simplified models. The beltdrives or the drive elements, output elements and transmission elementsare shown purely schematically at the main motor 9, at thesuperimposition motor 14, at the differential gear 10, at the pair ofscanning rollers 3 and at the roller combinations 6, 6′, 6″.

FIG. 2 shows a schematic view of an autoleveller draw frame 1 accordingto the invention. In comparison to the exemplary embodiment from FIG. 1according to the prior art, among other things, the differential gear 10has been removed and the superimposition motor 14 has been replaced by aregulating motor 17, which is drive-independent of the main motor 9 suchthat the regulating motor 17 drives the input roller combination 6 andthe middle roller combination 6′ independently of the main motor 9 atthe autolevelling speed on the basis of an electrical signal 18, whichdepends on the main rotational speed. The regulating motor 17 ispreferably in the form of a reluctance motor. The main motor 9 ispreferably in the form of an induction motor, and so this is driven at aconstant rotational speed.

A speed sensor 19 for detecting the rotational speed of the main motor 9and/or of the output roller combination 6″ is arranged in the area ofthe main motor 9 and/or of the output roller combination 6″ of theautoleveller draw frame 1 according to the invention. The speed sensor19 is electrically operatively connected, for example, by means oftransmission lines, to a transmission unit 20, which converts thedetected rotational speed into the basic rotational speed of the inputroller combination 6 and/or of the middle roller combination 6′ or intothe rotational speed of the regulating motor 17 required therefor.

In addition, the drive unit 8 of the autoleveller draw frame 1 accordingto the invention, in the exemplary embodiment shown in FIG. 2 , includesa control unit 21, which can calculate or control the autolevellingspeed of the regulating motor 17. For this purpose, the control unit 21is electrically operatively connected to the specification unit 15, tothe transmission unit 20 and to the regulating motor 17. The controlunit 21 calculates the autolevelling speed on the basis of the basicrotational speed from the transmission unit 20 and on the basis of thesuperimposition speed from the specification unit 15. The specificationunit 15 is preferably reused from the autoleveller draw frame 1according to the prior art.

When converting the autoleveller draw frame 1 according to the prior art(FIG. 1 ) into the autoleveller draw frame 1 according to the invention(FIG. 2 ), preferably at least one of the drive elements 11, 12 and/orone of the output elements 13 of the differential gear 10 is/are reusedas the transmission element 22 of the regulating motor 17. Thetransmission element 22 transforms the rotational speed of theregulating motor 17 such that the input roller combination 6 and themiddle roller combination 6′ are driven at the autolevelling speed. Theautolevelling speed of the input roller combination 6 and of the middleroller combination 6′ can also differ from each other in the exemplaryembodiment from FIG. 2 . In the present exemplary embodiment, the seconddrive element 12 of the differential gear 10 has been reused as thetransmission element 22 of the regulating motor 17. Due to the reuse ofthe second drive element 12 as the transmission element 22 of theregulating motor 17, the permanent gear ratios (according to FIG. 1 )used in the autoleveller draw frame 1 having the differential gear 10and the superimposition motor 14 can be very easily adapted to theautoleveller draw frame 1 having the independent regulating motor 17.

The present invention is not limited to the represented and describedexemplary embodiments. Modifications within the scope of the claims arealso possible, as is any combination of the features, even if they arerepresented and described in different exemplary embodiments.

LIST OF REFERENCE SIGNS

-   -   1 autoleveller draw frame    -   2 sliver    -   3 pair of scanning rollers    -   4 drafting system    -   6, 6′, 6″ roller combinations    -   7 fibrous web    -   8 drive unit    -   9 main motor    -   10 differential gear    -   11 first drive element    -   12 second drive element    -   13 output element    -   14 superimposition motor    -   15 specification unit    -   16 brake    -   17 regulating motor    -   18 electrical signal    -   19 speed sensor    -   20 transmission unit    -   21 control unit    -   22 transmission element

1-13: (canceled)
 14. An autoleveller draw frame, comprising: a draftingsystem having a plurality of roller combinations situated one behind theother for drafting a fibrous web from one or more slivers; a drive unitconfigured with the plurality of roller combinations, the drive unitcomprising: a main motor that drives a first of the roller combinationsat a constant main rotational speed; a regulating motor that regulates arotational speed of a second of the roller combinations, wherein, due tothe regulation, the rotational speed of the second roller combination ischangeable from a basic rotational speed into an autolevelling speed,the basic rotational speed depending on the main rotational speed andthe autolevelling speed being independent of the main rotational speed,wherein the drafting of the fibrous web is adjustable; and theregulating motor being drive-independent of the main motor to drive thesecond roller combination independently of the main motor at theautolevelling speed according to an electrical signal that is based onthe main rotational speed.
 15. The autoleveller draw frame according toclaim 14, wherein the drive unit comprises a speed sensor that detectsthe main rotational speed of the first roller combination or rotation ofthe main motor.
 16. The autoleveller draw frame according to claim 15,wherein the drive unit comprises a transmission unit that transforms asignal from the speed sensor into a signal for the basic rotationalspeed of the second roller combination.
 17. The autoleveller draw frameaccording to claim 14, further comprising a pair of scanning rollersthat detect a thickness of the slivers entering the drafting system. 18.The autoleveller draw frame according to claim 17, further comprising aspecification unit electrically connected to the pair of scanningrollers, the specification unit setting a superimposition speed for thebasic rotational speed based on the thickness of the slivers.
 19. Theautoleveller draw frame according to claim 18, wherein the drive unitfurther comprises a control unit configured with the regulating motor,the control unit calculating the autolevelling speed from thesuperimposition speed and the basic rotational speed.
 20. Theautoleveller draw frame according to claim 19, wherein the autolevellingspeed is transmitted to the regulating motor as an electrical signal.21. The autoleveller draw frame according to claim 14, wherein the mainmotor comprises an induction motor and the regulating motor comprises areluctance motor.
 22. A method for operating an autoleveller draw frame,wherein the autoleveller draw frame includes: a drafting system having aplurality of roller combinations situated one behind the other fordrafting a fibrous web from one or more slivers; a drive unit configuredwith the plurality of roller combinations, the drive unit comprising: amain motor that drives a first of the roller combinations at a constantmain rotational speed; a regulating motor that regulates a rotationalspeed of a second of the roller combinations, wherein, due to theregulation, the rotational speed of the second roller combination ischangeable from a basic rotational speed into an autolevelling speed,the basic rotational speed depending on the main rotational speed andthe autolevelling speed being independent of the main rotational speed,wherein the drafting of the fibrous web is adjustable; and the methodcomprising driving the regulating motor independent of the main motor todrive the second roller combination independently of the main motor atthe autolevelling speed on the basis of an electrical signal that isbased on the main rotational speed.
 23. A method for converting anautoleveller draw frame from an initial configuration to a finalconfiguration, the initial configuration including: a drafting systemhaving a plurality of roller combinations situated one behind the otherfor drafting a fibrous web from one or more slivers; a drive unitconfigured with the plurality of roller combinations, the drive unitincluding: a main motor for driving a first of the plurality of rollercombinations at a constant main rotational speed; a differential gearthat transmits a rotational speed of the main motor to a second of theplurality of roller combinations such a basic rotational speed of thesecond roller combination depends on the main rotational speed of thefirst roller combination; and a superimposition motor that superimposesa superimposition speed on the basic rotational speed by means of thedifferential gear such that, due to the superimposition, a rotationalspeed of the second roller combination is changeable from the basicrotational speed into an autolevelling speed; the method comprising:removing the differential gear from the drive unit; replacing thesuperimposition motor with a regulating motor that is drive-independentof the main motor; and wherein the regulating motor drives the secondroller combination independently of the main motor at the autolevellingspeed on the basis of an electrical signal that depends on the mainrotational speed.
 24. The method for converting an autoleveller drawframe according to claim 23, wherein at least one drive element oroutput element of the differential gear is reused as a transmissionelement of the regulating motor.
 25. The method for converting anautoleveller draw frame according to claim 23, further comprisingremoving a mechanical or electromagnetic brake of the drive unit.